Continuing investigation of the polydeformed Cambrian and
Ordovician rocks of the Miramichi Highlands in west-central New
Brunswick has led to an improved understanding of the stratigraphy of
the Cambro-Lower Ordovician Miramichi Group and overlying Ordovician
Tetagouche Group (van Staal and Fyffe 1991, 1995a, 1995b). Shelly
fossils, mainly brachiopods of late Arenig age, have been found in sandy
tuff, sandstone, siltstone and mudstone at several places within the
basal beds of the Tetagouche Group. In northwestern Napadogan area, the
tuff is underlain by oligomictic conglomerate whose quartzite clasts
were derived from the Miramichi Group. These basal Tetagouche strata
occur within the transition from a deep-water fan complex of quartzose
psammitic and pelitic turbidites of the Miramichi Group (Rice and van
Staal 1992) and deposition of the overlying volcanic-chertgreywacke
assemblage of the Ordovician Tetagouche Group, a transition representing
the change from a stable continental margin to an unstable volcanic
back-arc setting marked by rifting, local uplift and erosion, followed
by mainly felsic volcanism and subsidence. In the northeastern Miramichi
Highlands, these Lower-Middle Ordovician strata host the volcanogenic massive, base-metal sulphide deposits of the Bathurst mining camp (van
Staal et al. 1992; van Staal et al. in press). Mineral exploration
companies searched the Napadogan area for similar sulphide deposits and
for granophile Sn-W-Mo deposits mainly during the 1970s and 1980s. No
deposits justifying development were found and exploration has since
decreased. Perhaps the work reported here will help guide future
exploration to more prospective formations. The geology of the Napadogan
area is not known in as great a detail as is the Bathurst camp. The
results reported here may be a first step to improved comparisons and
integration of the stratigraphy and depositional and tectonic settings
of the rocks of the two areas.

Early surveys of the bedrock geology of the Napadogan area of
central New Brunswick outlined a broad belt roughly 40 kilometres wide,
of deformed and cleaved sedimentary rocks, lying between the granitic
plutons on the northwest and the flat-lying Carboniferous cover of
central and eastern New Brunswick (Robb 1870; Ells 1881). Robb collected
brachiopods at one locality (herein, the Rocky Brook locality) within
this extensive unfossiliferous area and they were interpreted as
Silurian-Devonian of the Gaspe Limestone series (Billings in Robb 1870,
p. 190). These fossiliferous rocks were "accommodated" on a
regional geological map as a "patch" of young strata of
unknown relations to the presumed Cambro-Silurian rocks (i.e. Ordovician
in later years; Bailey et al. 1886). Later, similar brachiopods were
found 25 km on trend to the northeast by Ells (1881) (herein, the Lower
Birch Island locality); the fossils were collected by Bailey (1906) and
interpreted as Silurian by Ami (1906).

Fifty years later, regional bedrock geological mapping by the
Geological Survey of Canada for publication at one mile to an inch
(Poole 1958, 1960, 1963; Anderson and Poole 1959) divided the
40-kilometre belt in two: a Cambrian-Ordovician belt (the Miramichi
terrane) and to its southeast, a belt of Silurian turbidites with a few
graptolite localities (the Fredericton Trough). The brachiopods of the
two early-found localities and a new locality (herein, the Middle Hayden
Brook locality) were firstly reinterpreted as Ordovician and later by
Neuman as probably late Arenig when compared to his collections from the
rich localities of eastern Maine in the Weeksboro-Lunksoos area and of
Newfoundland and Europe (Neuman and Bates 1978; Neuman and Harper 1992),
coupled with precise U-Pb zircon isotopic ages from related volcanic
rocks in the northeastern Miramichi Highlands. [For simplicity, we will
use "Napadogan area" to refer to the area of interest in the
Napadogan-Hayesville area of central New Brunswick, and to
"Lunksoos area" for the Weeksboro-Lunksoos anticlinorial area
of Maine, the latter following the lead of Boone and Boudette (1989, p.
29)].

During the late 1970s and early 1980s, Irrinki (1980, 1981) and
Crouse (1981a, 1981b) of the New Brunswick Department of Natural
Resources, remapped and refined the bedrock geology of mainly the
Miramichi terrane of the Napadogan and Hayesville map areas (21 J/07,
10). And finally, during the late 1990s, 2000 and 2002, Poole mapped
selected localities of Ordovician strata in detail mainly along roads
built for logging activities during the past 20 years.

In hilly, forested central New Brunswick, bedrock exposures are
sparse and generally small and of poor quality. Bedrock is exposed
mainly along streams and roads cut through a blanket of glacial till
ranging in thickness from a half metre or less on some hilltops to one
or two metres along flanks of most hills and several metres in broad
valley bottoms. Exposures along logging roads generally provide only
lithology from weathered rocks and some bedding and cleavage
measurements. Rarely are key stratigraphic and structural relations
helpfully displayed on cliffs. Distribution of bedrock units beneath
thin till is suggested by a rubble of bedrock broken by road-building
bulldozers.

Herein, we describe the Arenig strata in the Napadogan and Lunksoos
areas and compare them to strata in the northeastern Miramichi Highlands
(Fig. 1) to demonstrate some similarities and differences. We will
introduce new formation and member names for Arenig strata in the
Napadogan area, suggest interpretations of their modes of deposition and
then discuss the brachiopods from new localities discovered in the
Napadogan area during recent years.

For divisions of Ordovician time, we use the British series
Tremadoc, Arenig, Llanvirn (including Llandeilo stage), Caradoc and
Ashgill (Fortey et al. 1995). The time scale of McKerrow and van Staal
(2000) is used as a modern, reasonable approximation.

The northern two thirds of the Napadogan area (the
"Freehold") is currently owned and logged by Bowater Canadian
Forest Products Inc., Boiestown, New Brunswick. Access to the logging
road system leading north from the southern boundary, for day trips
only, is controlled by gatekeepers at Napadogan, Gordon Vale and McKiel
Brook.

Within some figure captions, GSC Photo xx refers to the photograph
collection of the Geological Survey of Canada, and GSC loc. xx refers to
the locality of a fossil collection registered with the Geological
Survey of Canada. The illustrated fossil specimens of Fig. 11 are in the
National Type Collection, Geological Survey of Canada, Ottawa.

REGIONAL TECTONIC SETTING

The current model of the regional tectonic setting of the rocks of
Napadogan and Lunksoos areas has been developed by many geologists
working in northern New Brunswick and northern Maine during the past
twenty years or more. Of course, unanimity has not been achieved. From
the view of the Miramichi terrane, syntheses by van Staal et al. (1992),
van Staal et al. (1998) and van Staal et al. (in press) list co-authors
who have contributed to the model. The view developed from Maine's
geology has been summarized by such authors as Boone and Boudette
(1989), Boone et al. (1989) and Berry and Osberg (1989). All these
syntheses contain extensive reference lists.

Rocks of the Napadogan and Lunksoos areas are linked to two
volcanic arcs that lay to the northwest (today's directions; van
Staal et al. 1998; van Staal et al. in press). The arc strata are well
exposed in Newfoundland but unfortunately are mainly covered in northern
New Brunswick although they are somewhat better exposed in northern
Maine. According to the above authors, the older, ensimatic Penobscot
Arc existed within Iapetus Ocean above a northwest-dipping subduction
zone during at least Middle Cambrian to Tremadoc. Tremadoc-early Arenig
collision with the northwest-subducting Gander margin (Ganderia; van
Staal et al. 2002a) with its cover of Miramichi strata (peri-Gondwana)
led to obduction of the arc perhaps as many as hundreds of kilometres to
the southeast. At least parts of the outer edge of the Gander margin
were then uplifted and rifted, and the obducted Penobscot Arc rocks
largely removed by erosion. Possible remnants of the arc rocks are
bimodal, within-plate and possibly subduction-related volcanic rocks in
the Annidale Group and subduction-related volcanic rocks of the New
River Belt, both of southern New Brunswick (McLeod et al. 1994; Johnson
and McLeod 1996), and of coastal Maine, bimodal, within-plate
continental rift volcanic rocks of the Ellsworth Schist (Stewart et al.
1995). However, all these formations occur within zones of
northeast-striking thrusts and strike faults near and within the complex
zones between the Gander margin, Brookville terrane and northwestern
parts of the composite Avalonian terrane that could well have involved
volcanic arcs and nearby back arcs (Barr and White 1996). Indeed, no
exposed remnant of the Penobscot Arc may exist in New Brunswick and
Maine, but samples may exist as clasts and heavy minerals in Arenig
conglomerates. A search for the tectonic setting of the source volcanic
rocks and indicator minerals such as chromite has not been conducted.

The younger, Popelogan volcanic arc started about early to middle
Arenig after obduction of the Penobscot Arc was completed (van Staal et
al. 1998; van Staal et al. in press). The subduction zone changed from
northwest-dipping during Penobscot time to southeast-dipping during
Popelogan time. Oldest rocks assigned to the Popelogan Arc are volcanic
rocks of the Meductic Group within the Miramichi terrane about 80 km
southwest of the Napadogan area (Fyffe 2001). The volcanic rocks grade
broadly from rhyolite stratigraphically upward to basalt and intruded
arc-setting granite, all of early to middle Arenig age, and include
intercalated green and maroon manganiferous chert and slate. The group
lies conformably upon black slate and siltstone of the Bright Eye Brook Formation containing late Tremadoc to earliest Arenig graptolites (Fyffe
et al. 1983; Pickerill and Fyffe 1999). The geochemistry of the volcanic
rocks suggests a change from base to top from a
compressional-continental arc setting to an extensional-continental arc
setting (Fyffe 2001). Arc volcanism ceased when the subduction zone
migrated northwestward as the extensional Tetagouche back-arc basin
opened on the Gander margin (including the Napadogan and Lunksoos
areas). Today, Lunksoos rocks lie 40 km to the northwest of southern
Miramichi terrane and the two areas are separated by mainly
Siluro-Devonian strata (Fig. 1). Lunksoos bimodal volcanic and
sedimentary rocks of the mainly late Arenig Shin Brook Formation
unconformably overlie slate and turbiditic quartzite of the Grand Pitch
Formation, the oldest rocks exposed. The geochemistry of a few of the
volcanic rocks suggests that they lie above a sialic crust probably in a
back-arc setting like that of northern New Brunswick (Winchester and van
Staal 1994) and probably like that of the Napadogan block (van Staal et
al. in press). If the age assignments are correct, the timing of
Meductic arc volcanism overlapped with a period of rifting, uplift and
erosion of Miramichi-Grand Pitch rocks in the back arc, and early to
middle Arenig volcanic rocks were not deposited in the back arc in the
Napadogan area. The Popelogan Arc rocks that are exposed in the
Popelogan inlier of northeastern New Brunswick consist mainly of
Llanvirn andesitic to basaltic arc rocks and early Caradoc black shales
(van Staal and Fyffe 1991). The volcanic rocks were produced when the
subduction zone migrated to the northwest due to rollback of the
southeastward subducting slab (van Staal et al. 1991). The Meductic and
Popelogan-inlier rocks developed to the northwest of the Napadogan and
Lunksoos areas. During the late Caradoc and Ashgill, the Popelogan Arc
was uplifted, obducted toward the northwest and amalgamated with the
Boundary Mountains terrane of northern Maine. The uplifted arc rocks
shed detritus that was carried in turbidity currents toward the
southeast upon the Gander margin (van Staal et al. 1998; van Staal et
al. in press). The rocks of the Napadogan and Lunksoos areas are a
sample of this back-arc basin.

In contrast, another interpretation developed by Boone et al.
(1989) and Boone and Boudette (1989), largely in northern Maine,
involves only one subduction zone between the Boundary Mountain terrane
and the Gander margin. The Hurricane Mountain Formation of mainly Middle
and Upper Cambrian strata, containing polymictic tectonic melange with
olistostromes, is interpreted as an accretionary wedge related to a
subduction zone lying south of the Boundary Mountains terrane and
dipping southeast beneath the Gander margin. The Boundary Mountains
terrane moved southeastward and became amalgamated with the Gander
margin during Late Cambrian to Early Ordovician, the Penobscottian
(Penobscot) orogeny. Taconian deformation later during the Ordovician
consisted of warping and local open folding and high-angle faulting.
Volcanic arc rocks related to the subduction zone were not identified
with confirming geochemistry. An amalgamated Boundary Mountain-Gander
terrane would have permitted Celtic brachiopods to occupy the Boundary
Mountains segment; none have been reported there. It seems more probable
that an ocean existed between the two terranes during the Arenig at
least. Thus, we prefer the Penobscot-Popelogan model of van Staal and
colleagues as described above.

MIRAMICHI GROUP OF THE NAPADOGAN AREA

The oldest rocks in the Napadogan area are deep-water, turbiditic,
interbedded slate and quartzite of the Miramichi Group, deposited during
the Cambrian and Tremadoc on the continental slope along the northwest
side of the Gander margin bordering the Iapetus ocean (Rice and van
Staal 1992; van Staal et al. in press). Light grey to greenish grey
slate and quartzite with some laminated siltstone occur throughout the
Napadogan area. Thin section study of several specimens reveals a
subgreywacke mix of quartz, plagioclase and matrix. Quartz grains are
generally subangular, 0.2 to 0.3 mm in diameter (fine- to medium-grained
sand) with "outsize" subrounded grains to 0.7 mm
(coarse-grained sand) with 6% to 16% plagioclase presumably albite, 10%
to 25% matrix of fine-grained secondary micas and metamorphic albite(?)
and traces of detrital muscovite, tourmaline (pleochroic colourless to
green to brown--schorlite?) and zircon (petrography and point counts by
Fred Harris 1961-62). The quartzite has characteristics of a turbidite,
and certainly not those of a mature, quartz beach sand. Only along the
northwestern side of the Napadogan area (Otter Slide belt, Fig. 2) does
the top unit of the group include black slate with minor dark grey
quartzite and dark grey greywacke containing exotic felsic volcanic
detritus (vitreous black quartz and bluish quartz grains) deposited in
anoxic deep water. Whether the black slate-quartzite-greywacke facies was deposited only in the strata of the northwestern belt or was
deposited throughout the Napadogan area and was removed by erosion
during the Tremadoc-Arenig is conjectural. We favour the former
alternative for reasons presented later in the paper. Further, perhaps
the dark grey slate unit was deposited in anoxic deep water while to the
southeast, higher on the continental slope, a light grey slate facies
was deposited in oxic water depths. The dark facies, which includes one
low outcrop on Turnbull Mountain of medium to dark grey fine pebble
conglomerate consisting of pebbles of medium to dark grey quartzite, 1
to 4 cm in diameter, in a dark grey pelitic matrix, probably signalled
deepening water as the Gander margin closed on the Penobscot Arc just
prior to Penobscot obduction during the Tremadoc-early Arenig (Fyffe et
al. 1983; van Staal et al. in press). The dark grey slate and light grey
slate facies are grossly interlayered. Perhaps the dark grey slate
facies with its volcanic detritus was derived from the deforming
Penobscot volcanic arc to the northwest while the light grey slate
facies was derived from the Gander margin to the southeast. Thus the two
facies became interlayered in a trough between deforming arc and
approaching margin in waters near oxic-anoxic depths.

Today, the Miramichi rocks core anticlinorial belts with infolded
and infaulted Ordovician strata, and many are surrounded by
Siluro-Devonian strata (Fig. 1). These old rocks, the oldest known
within the Miramichi terrane, were intruded by syn-volcanic Ordovician
granites (north of the Napadogan area) and were metamorphosed, deformed,
probably thrust southeastward, and intruded during post-mid-Ordovician
deformations. The three belts of Miramichi strata in the Napadogan area
are referred to as the Lower Hayden, Burnt Hill and Otter Slide belts
for easy geographic reference (Fig. 2).

TETAGOUCHE GROUP OF THE NAPADOGAN AREA

Overlying the Miramichi Group in the Napadogan area with presumed
local unconformity in the northwest but conformity or disconformity in
the southeast is the Arenig-Ashgill Tetagouche Group, a varied
sedimentary-volcanic assemblage representing the product of a volcanic
back arc and subsequent infilling, developed upon the Miramichi basement
cover of the Gander margin (van Staal 1994; van Staal and Fyffe 1995a).
Early Arenig uplift along the northwest part of the margin in the
Napadogan area was characterized by some tilting and warping without
folding, presumably along rift faults; one associated uplift, herein
referred to as the Napadogan uplift, exposed Miramichi Group strata to
erosion. Van Staal et al. (1991) attributed the uplift and disconformity
at the base of the Tetagouche Group (Vallee Lourdes Member) and
subsequent volcanism in the northeastern Miramichi terrane to
lithospheric doming associated with arc rifting and with rollback of the
subducting slab. In the Napadogan area, a coarse gravel of Miramichi
quartz sandstone was deposited there and along the northwest-facing
Iapetan margin and then probably slumped into deeper water (Upper
Buttermilk Member of the Turnbull Mountain Formation--new names). Soon
after, late Arenig felsic volcanism from distant sources deposited
several metres of sandy and silty tuff, and minor crystal tuff along
with mudstone in some localities, followed by minor local mafic tuff and
flows (Lower Birch Island Member of Turnbull Mountain Formation). The
volcanic deposits became overlain by a blanket of Llanvirn ferruginous and manganiferous, varicoloured slate and chert and during Caradoc, the
waters became anoxic (deeper?) and the slate and chert carbon-rich and
pyritic. Finally, during the late Caradoc and Ashgill, turbidity
currents began to fill the basin with dark grey mudstone and volcanic
greywacke derived from an uplifted and deforming Popelogan Arc to the
north (van Staa1 1994). Ten to 30 kilometres to the north and northeast
of the Napadogan area of this paper, felsic and mafic volcanic rocks are
more abundant (Poole 1963; Irrinki 1980, 1981), and some mafic volcanic
rocks contain blocks of Llanvirnian slate and chert.

Turnbull Mountain Formation

The Arenig conglomerate and late Arenig bimodal volcanic rocks and
sedimentary rocks are collectively herein named the Turnbull Mountain
Formation, comprising two subunits, the basal Upper Buttermilk Member of
quartzite conglomerate and the overlying Lower Birch Island Member of
felsic tuff and minor mafic tuff and flows, and sandstone varying to
siltstone and slate. The younger member has yielded brachiopods in seven
localities. The formation is named from Turnbull Mountain on which the
two members are exposed, 5 km north-northeast of the small community of
Napadogan (Fig. 2). All geographic names of new formations are
recognized by the Geographic Names Board of Canada.

Exposures of Turnbull Mountain strata have been found only there
and above Miramichi Group strata and below the overlying Llanvirn
slate-chert unit of the Tetagouche Group. No exposure displays strata of
both members from base to top. Thus, an ideal type section cannot be
identified. Currently, a type area enclosing several localities as
depicted in the Napadogan area of Fig. 2 must serve. The overall
stratigraphic sequence has been established by integrating parts of the
stratigraphy from these localities. This lack of continuity is
attributed to a combination of unrelated factors such as discontinuous deposition (especially of the Upper Buttermilk conglomerate), thrust and
strike-slip faulting during subsequent deformation, and generally sparse
exposures. It is impossible to determine with confidence, in any one
locality, which cause or combination of causes explains the presence or
absence of units.

The Turnbull Mountain Formation overlies the Cambrian and Tremadoc
Miramichi Group and is overlain conformably by Llanvirn slate-chert. The
formation is no more than 10 m thick at its thickest in the northwestern
Napadogan area. It is probably middle to late Arenig, an age derived
from brachiopods and conodonts in the upper member and, from the
northeastern Miramichi terrane U-Pb zircon isotopic ages of correlative volcanic rocks. Correlative formations are the Shin Brook Formation in
the Lunksoos area and Nepisiguit Falls Formation in the northeastern
Miramichi Highlands with its basal sedimentary Vallee Lourdes Member and
overlying volcanic Little Falls Member (van Staal et al. in press).

Upper Buttermilk Member

The Buttermilk Brook Formation was first named by Potter (1969) in
his unpublished Ph.D. thesis on the geology of the Burnt Hill area (in
the Burnt Hill belt of this paper), a few kilometres north of the
northern edge of the Napadogan area. The name was derived from a small
brook known by local people as Upper Buttermilk Brook in the 1960s, but
not then recognized by the Geographic Names Board of Canada. Another
brook, 5 km to the northeast was recognized by the Board as Buttermilk
Brook, where the formation apparently does not exist. Currently, the
names of both brooks are recognized by the Board. Irrinki (1981) applied
the name Buttermilk Brook to a small granite stock exposed along
Buttermilk Brook. Potter's name was later used in regional
syntheses, for example, by van Staal and Fyffe (1991, 1995a).

The name 'Upper Buttermilk Member' (of the Turnbull
Mountain Formation) is herein proposed to replace Buttermilk Brook
Formation of Potter (1969). The new name recognizes the nearby Upper
Buttermilk Brook and avoids confusion with the Buttermilk Brook granite
of Irrinki (1981). The term "brook" is omitted in accordance
with recommendations of the North American Code of Stratigraphic
Nomenclature and, more practically, to keep the name reasonably short.

Potter's type area is on the northwest side of a ridge, the
north end of which is 2 km south of the former Burnt Hill mine and 4 km
northeast of the Napadogan area, within the Burnt Hill belt (Fig. 2).
Along 2 km of the ridge to the southwest, sporadic metresize blocks of
conglomerate attest to their nearby bedrock source. However, at the
north end of the ridge is a large area of outcrop and slumped blocks on
a short bluff and steep slope, unseen by Potter (1969) but mapped by
Crouse (1981a). The site is on the northwest corner of the ridge, about
300 m south of an unnamed branch of the Upper Buttermilk Brook that
limits the ridge on the north. Despite that rocks stratigraphically
above and below the conglomerate are not exposed near this outcrop, this
locality is here designated the type locality. Unfortunately, access is
difficult; the nearest road suitable for motor vehicles is the Mine
road, one kilometre of bush and forest to the west.

Potter described the unit, speculatively about 250 m thick, as a
lower part of grey-green conglomerate with subangular to subrounded
pebbles (some larger than 4 cm) of quartz sandstone ([less than or equal
to]35%), siltstone (30%) and laminated quartz siltstone (<5%), and an
upper part of poorly sorted distinctively grey-green sandstone and
siltstone. Crouse (1981a), in the same area, described the conglomerate
as comprising angular to subrounded pebbles of siltstone, quartzose
sandstone and quartz wacke in a sparse phyllitic matrix; pebbles are
commonly 3 to 5 cm in diameter to a maximum of 25 cm. He observed that
the conglomerate is interbedded with light greenish grey siltstone.
Current geological mapping by Poole in the Napadogan area and in the
Burnt Hill belt has demonstrated that the conglomerate is probably no
more than several metres thick in most if not all localities, and
consequently the unit is designated as a member in this paper. Further,
Poole did not observe the siltstone interbeds of Crouse, and the
grey-green sandstone and siltstone of Potter is assigned to the upper
part of the Lower Birch Island Member.

In the Napadogan area, the Upper Buttermilk Member consists of
conglomerate that presumably rests sharply on Miramichi strata (the
basal contact has not been seen in the Napadogan area or anywhere in
central New Brunswick) and is from zero to perhaps several metres thick
(Figs. 2, 3, 4). One exposure east of Turnbull Mountain is 7 m wide
across structural trend but bedding is not visible. The conglomerate
consists of a light grey to green-grey, clast-supported pebble and
cobble quartzite, which range from granules to a maximum of 25 cm in
diameter, in a minor sandy matrix (Fig. 5). The clasts are well rounded
to subrounded, oblong to spherical, or slightly flattened by imposed
deformation, and they are clearly derived from the underlying Miramichi
Group. Absent are clasts of greywacke, feldspathic quartzite, medium to
dark grey quartzite and black mudstone, all characteristic of the
uppermost strata of the Miramichi Group in the northwestern-most
Napadogan area. Absent are any exotic rocks such as chert, granite and
volcanic and metamorphic rocks. Another notable absence are pebbles of
vein quartz and of quartzite clasts containing quartz veins before
erosion and deposition. Thus, evidence of penetrative deformation and
concomitant quartz-vein generation at the level of erosion in the source
area before or during uplift is lacking.

[FIGURE 2-5 OMITTED]

The conglomerate occurs sporadically within the Otter Slide and
Burnt Hill belts. It is absent in the Lower Hayden belt where the
younger Lower Birch Island Member rests conformably upon Miramichi light
grey slate and quartzite at the Lower Birch Island brachiopod locality
and almost assuredly elsewhere along the belt. The conglomerate is
notably massive and lacks bedding and interbeds as viewed close to the
outcrop. The conglomerate was probably derived from a gravel that
accumulated on fans off the mouths of streams cutting through a
rift-fault scarp exposing only the upper part of the Miramichi light
grey mudstone and lithified quartz sandstone. The lack of mudstone
clasts in the conglomerate attests to their weak lithification and
vigorous stream transport. The gravel was probably resedimented by
flowing en masse to the northwest down submarine canyons that cut
through the outer edge of the rifted uplift (the Napadogan uplift) into
a continental slope-type environment, like that described by Hubert et
al. (1970) for the emplacement of limestone conglomerates in the
Cambrian-Ordovician Quebec Group along the lower St. Lawrence River. In
the Otter Slide belt, the gravel came to rest upon the anoxic (deep
water?), dark grey mudstone, sandstone and wacke strata at the top of
the Miramichi Group and in the Burnt Hill belt, upon the less deep,
light grey mudstone and sandstone unit. Furthermore, it seems that the
rift faults accompanying the uplift probably occurred in a relatively
narrow belt of the light grey slate facies. The conglomerate formed a
series of fans, now appearing as lenses, that thin and pinch out along
strike. The basal contact of the conglomerate probably displays a sharp
contact, disruption of the immediately underlying beds and incorporation
of fragments of the underlying beds in the basal part of the
conglomerate. This model is preferred to one that involves widespread
uplift of the Gander margin and removal by erosion of the uppermost
strata of the Miramichi Group (plus any or most obducted Penobscot Arc
rocks). In the northeastern Miramichi Highlands, van Staal et al. (in
press) favour a disconformity at the base of the Tetagouche Group that
represents "significant local erosion" to explain "large
variations in thickness and local absence" of the uppermost
formation of the Miramichi Group throughout the Bathurst area (van Staal
et al. 2002b).

Correlation of Upper Buttermilk Member

In the Lunksoos area, the Shin Brook Formation consists mainly of
felsic volcanic rocks and their sedimentary equivalents, but at one
locality southeast of Roberts Mountain, the basal 3 m of the formation
is quartzite conglomerate with round quartzite clasts as large as 25 cm
in diameter (Neuman 1964, 1967). The conglomerate appears to be
lithologically identical to the conglomerate in the Napadogan area
(judging from one large specimen provided by Gary M. Boone, 2000) and
may well have been formed in the same manner. However, several
kilometres along strike to the northeast in the Island Falls quadrangle,
a lens of conglomerate, basal to the Shin Brook Formation and as thick
as 30 metres, consists of pebbles of felsite, quartzite and slate in a
chlorite-rich sandstone matrix (Ekren and Frischknecht 1967). Locally,
the conglomerate contains "boulder-size fragments of diverse
volcanic rocks and quartzite" (p. 5). If indeed the conglomerate of
the Shin Pond and Island Falls quadrangles are equivalent in
stratigraphic position and age, they demonstrate a great variation in
source rocks in rather close-by localities. The source of volcanic rocks
must have been nearby but these "phantom" volcanic rocks have
not been recognized. The crystal tuff reported in the Grand Pitch
Formation of the Shin Pond quadrangle along Seboeis River (Neuman 1967,
p. 6) has been reinterpreted as a non-volcanic sediment by Neuman. E.B.
Ekren (written communication 2002) confirms that the polymictic
conglomerate lies stratigraphically at the base of the Shin Brook
Formation. An interpretation must accommodate the areal variation of
clast lithology.

In the northeastern Miramichi Highlands along the "upper"
Tetagouche River, the basal bed of the Vallee Lourdes Member in the
Little Falls section is a fine-grained pebble conglomerate, 0.5 m thick,
consisting of 90% pebbles (1-2 cm in diameter) in a quartzcalcite
matrix, that rests sharply on the Patrick Brook Formation (there, the
uppermost unit of the Miramichi Group) consisting of dark grey greywacke
and black slate with some melange of disrupted quartz greywacke
suggestive of submarine slumping (Fyffe et al. 1997). The pebbles are
dark grey quartzose greywacke derived from the Patrick Brook Formation.
Gradationally above the conglomerate are 20 m of calcareous sandstone
and minor pebbly sandstone, that is in turn gradationally overlain by 5
m of limestone and siltstone that have yielded Arenig-Llanvirn conodonts
and a few crinoid fragments (Nowlan 1981; Fyffe et al. 1997). Three
kilometres to the west-southwest upstream along the river, the
stratigraphically equivalent conglomerate in the Patrick Brook section,
consisting of granules and fine pebbles, is overlain by calcareous
siltstone that has yielded middle to late Arenig brachiopods discovered
by L.R. Fyffe in 1973 (Neuman 1984; Fyffe et al. 1997). It is
interesting that there, the clasts in the conglomerate consist of 70%
quartz in contrast to the 100% dark grey quartzose greywacke in the
nearby Little Falls section. By further contrast, on the
"lower" Tetagouche River near Vallee Lourdes about 9 km
east-northeast downstream of the Little Falls locality, the Vallee
Lourdes conglomerate, interpreted to be a debris flow (Rice and van
Staal 1992), contains a few large rounded, Mesoproterozoic, unfoliated
and foliated granodiorite clasts as much as a metre in diameter and
abundant quartz phenoclasts derived from felsic volcanic rocks (van
Staal et al. 1996) along with clasts of quartzite and felsite (Skinner
1974). The granodiorite clasts are interpreted to be a sample of
possible basement to the Miramichi Group (Gander Zone) and the basement
to be Avalonian or other Gondwanan, not Laurentian (van Staal et al.
1996). Finally, a lens of Vallee Lourdes conglomerate near Middle River,
about 8 km west-southwest of the Patrick Brook locality, contains felsic
volcanic clasts (C.R. van Staal, oral communication 2002).

The conglomerate appears to rest sharply on the Miramichi and Grand
Pitch strata in the few localities where the contact was observed or the
interval covering the contact is narrow. Neuman (1964) first reported
that the sharp contrast in lithology and style of deformation above and
below the Shin Brook-Grand Pitch contact was evidence of an angular
unconformity representing part of Early Ordovician and much of the
Cambrian time. Neuman (1967) named the interpreted event the Penobscot
disturbance that later was called the Penobscot or Penobscottian orogeny
especially when applied to obduction of the Penobscot Arc (Boone and
Boudette 1989; Boone et al. 1989; Berry and Osberg 1989; van Staal et
al. 1998; van Staal et al. in press). Erosion of a possibly uplifted
Gander margin during the Tremadoc-early Arenig may have removed
extensive Miramichi strata and obducted arc before deposition of the
middle to late Arenig conglomerate and volcanic rocks of the Napadogan
and Lunksoos areas. In an alternative hypothesis, one we favour, a rift
or a relatively narrow zone of rifts, to the southeast of the Lunksoos
area and to the southeast of the Otter Slide-Burnt Hill belts of the
Napadogan area during their pre-thrust, Arenig time, was associated with
local uplift of Miramichi-Grand Pitch strata to erosion, the Napadogan
uplift in the Napadogan area. The resulting quartz-sandstone gravel
probably slumped through local submarine canyons toward the northwest.
Fine-grained quartzose and pelitic sediments in the Lower Birch Island
Member of the Lower Hayden belt were derived from the Napadogan uplift
to the northwest or possibly, from the southeast as a continuation of
Miramichi sedimentation. No convincing direct evidence of
pre-unconformity deformation other than simple uplift and tilting has
been described in the Miramichi Highlands. Arenig erosion probably
removed only the upper, non-penetratively deformed strata and
penetrative deformation and quartz veining, if any, occurred at deeper,
untapped levels. Finally, evidence of erosion of structurally overlying,
obducted Penobscot Arc volcanic rocks may be the volcanic clasts in the
Arenig conglomerate such as in the northeastern Miramichi Highlands and
the Island Falls quadrangle.

The lithology and maximum size of the clasts of the Arenig
conglomerate in the Lunksoos area and the Miramichi Highlands are
intriguingly varied from place to place. They range from pebbles and
cobbles of simple quartzite (Shin Pond quadrangle and Napadogan area),
to small pebbles of quartz and greywacke (upper Tetagouche River), to
cobbles and boulders of diverse volcanic rocks and quartzite (Island
Falls quadrangle), to cobbles and boulders of quartzite, felsite and
basement granodiorite with felsic volcanic detritus (lower Tetagouche
River at Vallee Lourdes). The differences are marked over only a few
kilometres (e.g., Shin Pond and Island Falls quadrangles and along the
Tetagouche River), but not every few kilometres witnesses changes (e.g.,
the Otter Slide and Burnt Hill belts of the Napadogan area and farther
north). The thickness of the conglomerate seems to increase with an
increase in average and maximum clast size (except perhaps the Vallee
Lourdes locality).

The variability supports the hypothesis that the conglomerate
originated near local rift faults accompanied by major subaerial uplift
with erosion by vigorous streams through fault scarps. The uplift would
probably be relatively narrow, wide enough to develop substantial
streams but not so wide as to encompass the entire back arc. Cobbles and
boulders could not have been transported far along streams or beaches,
as for example those at Vallee Lourdes and the Island Falls quadrangle,
and probably formed initially close to a major uplift with the
accompanying rift faults with substantial vertical displacements. The
rift near Vallee Lourdes may have brought up to erosion samples of the
basement beneath the Miramichi strata during Arenig time and may have
had the greatest throw. The volcanic clasts and detritus in these two
localities may have been derived from three possible sources: from
volcanic rocks intercalated in the upper layers of the Miramichi-Grand
Pitch strata (a possible local source only, given the general absence of
such volcanic rocks in present-day strata, but probably not in these two
localities); from obducted Penobscot Arc rocks lying structurally above
the Miramichi-Grand Pitch strata (quite plausible but the age and
tectonic setting of the volcanic clasts must be determined by isotopic
and geochemical analyses); and from hypothetical volcanic rocks formed
along the rifts and essentially the same age as the conglomerate
(theoretically possible but judged improbable because volcanic strata
are lacking in the conglomerate units). We are intrigued by the second
suggestion: Penobscot Arc rocks. Perhaps the volcanic clasts in the
conglomerate are a confirmation of the former existence of an overlying
obducted Penobscot Arc.

The pebbles and cobbles of quartzite of the conglomerates of the
Shin Pond and Napadogan areas are interpreted to have formed close to
rift-related uplifts but with perhaps less throw than the rifts near
Vallee Lourdes and Island Falls and then resedimented via submarine
canyons. Heavy-mineral concentrates from the conglomerates should be
searched for minerals indicating ophiolitic and volcanic arc sources.
The lack of volcanic clasts suggests that possible obducted Penobscot
rocks were removed by erosion before deposition of the quartz sandstone
gravel, or they did not exist in the vicinity. The proximity of Shin
Pond simple conglomerate and Island Falls polymictic conglomerate is
remarkable. Finally, the thin conglomerates with small pebbles of
greywacke and quartz in the upper Tetagouche River must have been
deposited farther out on the flank of the uplift and in shallow, warmer
water favouring deposition of limestone. The greywacke clasts are of
local origin but the source of the quartz clasts, from vein quartz, is
puzzling. Could quartz-veined rock have been brought up from the
basement?

The massive character of the conglomerates of the Napadogan and
Lunksoos areas, their lenticular distribution and the general lack of
intercalated finer sediments lend strong support to the hypothesis that
the conglomerates were resedimented by debris flow(s) through submarine
canyons into deeper water.

Lower Birch Island Member

Calcareous siltstone with minor felsic tuff and brachiopods on the
Southwest (S.W.) Miramichi River was first named the Lower Birch Island
Formation in regional syntheses by van Staal and Fyffe (1991, 1995a).
The description in this paper is the first to describe the unit and to
assign the beds as a member of the Turnbull Mountain Formation. The name
is derived from Lower Birch Island in the S.W. Miramichi River, about
300 m north (upstream) of the mouth of McBean Brook. The type section is
well exposed about 400 m north of the island on the east shore of the
river (Fig. 6). The exposures can be reached reasonably easily. A bush
road off the main Rocky Brook road leads west and down to the east shore
of the river, at a point about 150 m north of the island. The type
section is a 250-m walk north along the shore.

[FIGURE 6 OMITTED]

Irrinki (1980) placed the fossiliferous siltstone unit (i.e. Lower
Birch Island Member) within the top of the Miramichi Group and described
the unit as "calcareous slate containing 3-5 cm thick lenticular
tuff beds" (p. 7). He placed the top of the unit at the base of the
conformably overlying "red grit approximately 1 m thick containing
calcareous siltstone pebbles" (p. 9) that passes upward into maroon
slate of the overlying formation. This paper differs in lithological
determinations and placement of that contact.

The type section, 6 metres thick, is well exposed in a clean, large
outcrop rising from the river edge. It consists mainly of foliated,
light grey to greenish grey, calcareous siltstone and silty slate that
is uniform and lacks bedding (Figs. 6, 7). Fine detrital muscovite is
common. Sericite defines the curved foliation surfaces. Two foliations
separated by 20 to 30 degrees were observed by hand lens. Nodules of
more highly calcareous siltstone with gradational perimeters are evenly
distributed throughout most of the siltstone (Fig. 7). Most pits from
weathered-out nodules are a few centimetres across but some are as much
as 10 cm long and 5 cm wide. The nodules are slightly compressed
parallel to the main foliation. None are arranged to suggest remnants
(boudins) of once-continuous beds, although the long dimension of a few
nodules is aligned at a high angle to the main foliation. A few
brown-weathered fragments of beds of calcareous but more quartzose
siltstone displaying faint laminae suggest flow in the host siltstone
has broken the beds, pulled fragments apart by 10 to 30 cm, and slightly
rotated them. Coarse recrystallized calcarenite occurs in lenses within
a few metre-size slabs and smaller blocks of siltstone that have slid
downslope to the shore about 25 m south of the shore outcrop. The lenses
are less than 3 cm thick and pinch out in silty slate in 20 cm or less.
Contact of the calcarenite and enclosing slate is sharp. The siltstone
in one thin section consists of about 30% subangular to subrounded
quartz grains, 0.02 to 0.05 mm in diameter and only slightly deformed
(wavy extinction under crossed nicols), within a matrix of very
fine-grained micas and a trace of detrital muscovite in thin plates less
than 0.5 mm across. Crystalline calcite in part of the thin section
cements the siltstone and contains some thin curved plates suggestive of
cross-sections of fossil shells.

[FIGURE 7 OMITTED]

Lenses of thin beds of tuff, generally a centimetre or two thick
and constituting less than 5% of the unit, are intercalated mainly in
the middle and upper part of the siltstone, mark the bedding in the
siltstone, and pinch out in tens of centimetres. Two types of tuff are
present. The most common is a foliated, quartz-feld-spar-crystal tuff in
which the grains of uniform size are a millimetre or less in diameter.
In thin section, feldspar crystals are equant, 0.2 to 0.5 mm in
diameter, subrounded to subangular and completely altered to untwinned
albite and fine-grained micas. Feldspar is much more abundant than
quartz. Quartz is clear, undeformed, equant and subrounded to
subangular. Some grains have scalloped, corroded edges. Sericite defines
the foliation and envelopes the quartz and feldspar grains. The rarer
type of tuff is a foliated, green-grey aphyric felsite with a
porcelain-like texture. Weathered, disseminated, very fine-grained
pyrite imparts a limonitic coating. A few small brachiopods occur in the
siltstone and within the calcareous nodules. Those that appear as moulds
on the clean surface of the shore outcrop seem to have remained
uncompressed during deformation although perhaps broken as Ami
("fragmentary"; 1906, p. 291A) and Bailey ("much
distorted"; 1906, p.281A) noted.

Both the upper and lower contacts of the Lower Birch Island Member
are interpreted as conformable. The lower contact with the Miramichi
Group strata at the river's edge has been offset several metres to
the west, into the water, by an east-trending, steep, left-lateral cross
fault. But the contact is well displayed in cliff exposures on a steep
slope discovered during 2002 about 25 m south of the shore outcrop and
about 8 m above the shore. The immediately underlying strata of the
Miramichi Group consist of a thin light grey slate with fine detrital
muscovite overlying coherent, brittle-fractured, medium-bedded
quartzite. The quartzite superficially resembles a cobble and boulder
quartzite conglomerate (one "boulder" as large as a curling
stone) but sawcut surfaces by L.R. Fyffe clearly revealed the
non-sedimentary, fracture structure. The Lower Birch Island Member lying
above the thin slate and fractured quartzite consists of about 0.6 m of
slightly calcareous siltstone lacking more-calcareous parts, that grades
upward into typical wavy-foliated calcareous siltstone with sericitic
foliation surfaces, fine detrital muscovite and more-calcareous lenses
and nodules. The lenses of calcarenite in the slabs on the shore were
not located in the outcrop. The siltstone-slate contact appears
conformable and apparently not gradational through interbedding. A
depositional hiatus may exist between the two sequences.

The upper contact of the Lower Birch Island Member is exposed in
two nearby outcrops at the type section--on the shore and in the cliffs.
The contact in this paper is placed at the top of the one metre of
intercalated tuffaceous beds, in contrast to Irrinki (1980) who placed
the contact at the bottom. Thus, all the tuff in these exposures is
placed in the Lower Birch Island Member, and the overlying maroon
formation lacks tuff and calcareous siltstone in these exposures.
Further, the "red grit with siltstone pebbles" of Irrinki
(1980) is interpreted herein as coarser tuff rather than a sediment that
would imply a disconformity and erosion. Between the maroon slate above
and the light grey calcareous siltstone below is a metre or more of
interbedded siltstone, maroon ferruginous slate and sandy tuff. The
interbedding in this transition zone conceivably could have resulted
from structural interleaving from bedding-parallel movement, but we
doubt it. The siltstone and tuff in this transition zone are reddish
grey, presumably stained by hematite from the intercalated and overlying
maroon beds during weathering. Of interest is that fine detrital
muscovite occurs in both the Miramichi strata and the Lower Birch Island
siltstone, which along with the conformable relations, suggests that
Miramichi deposition from a southeastern source may have continued into
Lower Birch Island deposition in the Lower Hayden belt. However, we
suggest that both silt and brachiopods were derived from the eroding
Miramichi strata in the Napadogan uplift to the northwest.

The calcareous siltstone was probably deposited in quiet waters at
or below wave base near colonies of brachiopods in water depths not as
deep as that envisaged for Miramichi strata. Movement along the older
foliation surfaces would account for the lenticular nature of the
intercalated tuff and calcarenite beds. The younger, main, foliation
intersected the tuff beds at about 30 degrees to the beds without
significant attenuation or dismemberment parallel to the foliation and
did not flatten the brachiopods or the calcareous nodules appreciably.

Alternatively, the calcareous siltstone may have been deposited as
mass grain flow(s) (as suggested by L.R. Fyffe in discussion with Poole
at the type section, 2002). Consistent with this hypothetical
interpretation are features such as the lack of bedding in the
siltstone, lenticular nature of the tuff beds as if pulled apart by
grain flow or bedding-parallel movement, intercalated fragmented
siliceous siltstone beds, and broken brachiopods. Thus, the tuff beds
would have been pulled apart in a weak silt-water medium during final
emplacement by mass slumpage rather than by penetrative deformation.

Distribution of Lower Birch Island Member

The Lower Birch Island Member, like the underlying Upper Buttermilk
Member in the northwest, varies from place to place throughout the
Napadogan area in its lithology, apparent thickness and its presence or
absence along its stratigraphic horizon (Fig. 8). The felsic tuff is
commonly thin, soft and easily eroded, is thicker in northwestern
localities and has yielded brachiopods (Fig. 2). Mafic tuff occurs at
the top of the member in several localities and a mafic flow in two
other nearby localities. Sandstone and slate with brachiopod shells
underlie felsic tuff in one locality in the northwest. Mudstone and
siltstone with brachiopods dominate in the southeast. The member is
distributed as follows (Fig. 2): a) along the faulted southeastern
border of the Lower Hayden belt are two exposures of Lower Birch Island
rocks, preserved in fault horsts or enclaves sheltered from the master
fault, the Bamford Brook Fault (Poole 1963; Irrinki 1980; Fyffe 1982);
b) along the faulted southwestern end of the Burnt Hill belt are several
fault slices carrying the member; and c) along the faulted southeastern
edge of the Otter Slide belt are several fault slices with the member,
three of them fossiliferous.

[FIGURE 8 OMITTED]

Lower Hayden belt

Fossiliferous Lower Birch Island Member occurs in two enclaves
along the Bamford Brook Fault on the southeast side of the Lower Hayden
belt (Figs. 2, 8). On the lower parts of the Middle Hayden and nearby
Lower Hayden brooks, about 19 km southwest of the Lower Birch Island
type locality, the Lower Birch Island Member consists of about 6 metres
of steeply dipping, thin-bedded, medium grey calcareous argillite, silty
argillite and siltstone, overlying the Miramichi Group on the northwest,
conformably and perhaps gradationally. Along Middle Hayden Brook, the
underlying exposed Miramichi strata consist of about 45 m of open but
complexly folded, thin-bedded, light grey to greenish grey, slaty argillite and laminated siltstone with intercalated quartzite in thin to
medium beds. Calcareous argillite in the top 0.5 m of the 6-metre
sedimentary sequence of the member bears brachiopods and conodonts, the
Middle Hayden fossil locality (Fig. 2). The contact between the
Miramichi strata and the Lower Birch Island argillite and siltstone is
difficult to identify because the lithology of the two units is similar
although exposures along the brook are excellent. Strata with quartzite
are assigned to the Miramichi Group and those at the top of the sequence
lacking quartzite and more calcareous are assigned to the Lower Birch
Island Member. All these strata lack volcanic detritus and tuff. The
fossiliferous strata are faulted on the southeast against basalt
(5-metre covered interval) that is tentatively assigned to the upper
part of the Lower Birch Island Member. The basalt is in turn faulted
against Caradoc graphitic slate-chert on the southeast. The basalt is
light green-grey, mildly schistose, medium- and fine-grained, and
aphyric, from 50 to 80 m thick (if it is monoclinal and dips 60
degrees), and extends for about 5 km along strike. One flow or more may
exist; outcrops are discontinuous and flow contacts are not exposed
along the Middle Hayden Brook or Upper Hayden Brook. White and in places
red calcite and chlorite fill amygdules in part of the flow (of flows).
The rock has been thoroughly altered to a greenstone assemblage of
albite, epidote, chlorite and sericite.

In the second enclave, about 18 km farther to the southwest on an
unnamed small tributary of Rocky Brook, occur 3.5 metres of steeply
dipping, interbedded, light yellow-grey to light grey argillite,
calcareous argillite and minor siltstone. These strata are assigned to
the Lower Birch Island Member, are faulted against Caradoc graphitic
slate-chert on the southeast and, on the northwest, are separated by a
covered interval of several tens of metres along the tributary from
thin-bedded, greenish grey slate and thin-bedded quartzite of the
Miramichi Group. Much of the argillite contains disseminated, very
fine-grained pyrite, that with the abundant pyrite in the nearby
slate-chert, on weathering, has leached the carbonate and brachiopods
from the rock. No tuffaceous strata or tuff were observed although
possibly some of the very fine-grained "argillite" may have a
volcanic component. The fossil layer, the Rocky Brook fossil locality
(Fig. 2), occurs near the stratigraphic top (southeast side) of the
argillite near the fault and is difficult to locate. The weathered top
of the outcrop, a "brown pulverulent mass", yielded
brachiopods from a 5-cm layer (Robb 1870, p. 190). Such thin, soft,
easily eroded strata may well exist along the southeastern edge of the
Lower Hayden belt in undiscovered enclaves preserved along the Bamford
Brook Fault.

Along the northwestern edge of the Lower Hayden belt, Llanvirn and
Caradoc strata, younging northwest, overlie Miramichi slate and
quartzite and Arenig strata, if present, are not exposed. The Turnbull
Mountain Formation was observed in only one road crossing along 40 km of
the Miramichi-Llanvirn contact. There, along a logging road between the
headwaters of the Middle Hayden and Lower Hayden brooks (Fig. 2), a few
metres of rubble of altered mafic volcanic rock assigned to the Lower
Birch Island Member lies between Miramichi Group slate-quartzite rubble
and Llanvirn medium grey chert-slate rubble. The volcanic rock is a
granular, fine- to medium-grained, aphyric, light green-grey assemblage
of untwinned, bent and broken albite, much chlorite in aggregates and
microveinlets, and some epidote and titanite as seen in thin section. It
seems probable that Lower Birch Island strata exist along some or much
of the northwestern edge of the Lower Hayden belt, perhaps in part
lithologically similar to those of the Lower Birch Island locality.

Burnt Hill belt

A belt of the Turnbull Mountain Formation, Llanvirn grey-maroon
slate-chert and Caradoc graphitic slate-chert in the Burnt Hill belt,
lying between the Miramichi Group strata on the northwest and the
Caradoc-Ashgill slate-greywacke on the southeast (Fig. 4), extends for
10 km from the Upper Hayden road northeasterly to the S.W. Miramichi
River and beyond (Poole 1963; Crouse 1981a; Irrinki 1981). At the
southwest end, in the Napadogan area, these rocks for about 5 km between
the Upper Hayden and Mine roads consist of narrow wedge-like fault
slices of strata trending northeast, and lying northwest of the
east-northeast-trending master fault adjoining slate-greywacke (Figs. 2,
4). The Burnt Hill belt pinches out towards the southwest in a
"tail" of graphitic slate-chert marking the trace of the
master fault within the broad area of slate-greywacke (Fig. 2).

Felsic tuff occurs in five thin fault slices in the Burnt Hill belt
and all but the southeasternmost one pinch out toward the northeast in
thin-bedded Miramichi Group slate and quartzite along strike faults
(Fig. 4). The tuff is light greenish grey, weathered to buff to light
brown and consists of foliated quartz-crystal tuff with crystals less
than 2 mm in diameter, grading to massive, aphyric sandy and silty tuff
to lapilli tuff with very fine-grained aphyric fragments. The fragmental character of the tuff is visible only on clean weathered surfaces. In
thin section, quartz crystals are equant, clear and undeformed, and in
one thin section of a lithic lapilli tuff, a quartz crystal is a stubby bipyramidal prism, the high temperature form. In some varieties, quartz
crystals "float" in a very fine-grained, foliated
sericite-chlorite matrix that curves around the crystals and that
supposedly was fragmental before alteration and deformation. Rare
feldspar crystals have been altered to untwinned albite, sericite and
chlorite. All these rocks are rich in clay from Quaternary weathering.
Traces of pyrite have weathered to limonite and coloured the rocks a
light orange-brown. Mafic tuff, massive, schistose, medium green to
green-grey, appears in the fault slice along the southeast side,
adjacent to the Llanvirn strata. Clasts in the fine ash are in the 0.1
to 1 mm range and consist mainly of very fine-grained chlorite and some
carbonate. Feldspar has been altered to mainly sericite. The matrix
contains chlorite, sericite, epidote and calcite with rare equant quartz
crystals rimmed with chlorite. The thickness of strata in the slices is
impossible to estimate. Cross-strike widths of formations vary from zero
to 300 m and undetected internal repetition by fault-slicing in the
thicker sections is most probable.

An unusual fossiliferous sediment, tentatively assigned to the
Lower Birch Island Member, occurs along an old logging road about 0.7 km
south of the junction of the Mine road and the Lower Hayden road (Fig.
4). There, rubble along 11 metres of road aligned across the bedrock
strike consists of light greenish grey, mudchip quartz sandstone and
some granule conglomerate interbedded with light greenish grey slate and
siltstone. The chips and granules consist of silty mudstone and
siltstone, indicative of vigorous water flow. These rocks lack volcanic
detritus and have some detrital muscovite. The sandstone and
conglomerate weather readily to orange-brown to medium brown (limonitic)
from a percent or two of iron-bearing carbonate cement and pyrite in the
matrix. A few brachiopod fragments were found in the mudchip sandstone
within a few metres stratigraphically below crystal tuff (the Headwaters
of the Middle Hayden fossil locality, Figs. 2, 4). These strata,
unfortunately poorly exposed, are unlike other strata that host
brachiopods in the Lower Hayden belt, and until more exposures are
examined, they remain somewhat enigmatic.

Otter Slide belt

About 4 km to the southwest of the Burnt Hill belt, in the Turnbull
Mountain-Otter Slide Mountain area (Figs. 2, 3), Miramichi Group slate
and quartzite have apparently been thrust eastward against
Caradoc-Ashgill slate-greywacke. Between these two units are narrow
discontinuous fault slices of the Turnbull Mountain Formation and
younger Ordovician units. The Lower Birch Island Member consists of
massive, very fine-grained, aphyric, light greenish grey to grey to
ivory, fine- to coarse-grained felsic lithic tuff with disseminated fine
pyrite, and massive "argillite" that is white-weathering and
probably a very fine-grained tuff, perhaps originally a volcanic dust.
The "argillite" is medium to light grey and very weakly
foliated. Porphyroblasts likely of calcite in the form of thin plates
are characteristic; some have a hexagonal outline, and all have been
removed by weathering. The plates, as much as perhaps 5% of the rock,
are generally 2 mm in diameter and 0.1 to 0.3 mm thick. They are clearly
younger than the foliation, and thus may be related to emplacement of
the Devonian granite to the west. Three discontinuous slices have
yielded fossils but such have not been found in six nearby subparallel
slices. Thin mafic tuff overlies the felsic tuff in one slice.

The next westerly occurrence of Lower Ordovician felsic volcanic
rocks lies several kilometres to the west of the southern extension of
the Otter Slide belt, in the headwaters of Napadogan Brook (Lutes 1981),
outside of the Napadogan area discussed here. C.R. van Staal (oral
communication, 2002) believes that these Napadogan Brook volcanic rocks
are an extension of the Meductic Group from the south (Fyffe 2001) and
not a continuation of the Lower Birch Island Member. Their early to
middle Arenig age along with the geochemistry of the volcanic rocks
(Fyffe 2001), help distinguish them from Lower Birch Island volcanic
rocks.

Lithology and Origin of the shell beds

What lithological terms to apply to the brachiopod-bearing volcanic
rock in the Napadogan area is uncertain, and depends upon the envisaged
mode of formation of the fossiliferous rock. On the outcrop, the rock
appears massive except for layers of shells. In thin section, it appears
commonly fine-grained (<0.1 mm in some localities with quartz as
large as 0.5 mm), equigranular and massive, and appears to consist
mainly of clay and quartz with some limonite after disseminated
fine-grained pyrite cubes. All components appear to be felsic volcanic
rock. We suggest that the bulk of the host rock was probably airborne
volcanic ash and dust that settled in marine waters below wave base. If
this interpretation is correct, the applied lithological terms should
emphasize the pyroclastic origin rather than a sedimentary one. For that
reason, we use terms such as sandy, silty and clayey tuff. Tuffaceous
sandstone and related terms imply that the rock consists substantially
of detritus derived from weathering products, that the source rock was
weathered subaerially, that water action was significant and that the
resultant deposit is bedded.

Shell beds, in unusually high concentrations, occur within the Shin
Brook Formation (Fig. 9) and in the Lower Birch Island Member of the
Otter Slide belt. Brachiopods in each unit are concentrated in layers
dominated by a single species within otherwise massive sandy tuff. Most
brachiopod valves are unbroken and unabraded, and are oriented in a
hydraulically stable, convex-side-up position. Ventral valves outnumber
dorsal valves by perhaps 10 to 1; presumably the normally highly
indented dorsal valves were washed away from of the site. Thus, water
currents sorted and oriented the valves but did not break or abrade them. In a large block from the Lunksoos area (Figs. 9, 10), a few
shells immersed in a 5-cm layer of sandy tuff are aligned at about 45
degrees to the shell beds lying above and below, suggestive of internal
soft-stage movement after initial deposition. The upper shell bed of the
specimen has slid subparallel to bedding, crumpled and ridden upward 3
cm.

[FIGURE 9-10 OMITTED]

Kidwell and Aigner (1985) studied shell beds in Miocene strata in
Maryland, U.S.A., and concluded that the shells became concentrated from
normal concentrations by winnowing of the accompanying fine-grained sand
matrix. Kidwell (1986) explained some shell concentrations to result
from variation of sedimentation rate while the rate of production of
shells remained more or less constant.

It appears that in the Shin Brook shell beds of Figs. 9 and 10,
water currents did not play a major roll in sedimentation of the tuff
since mineralogical bedding did not develop, but gentle currents
prevailed. Winnowing was probably not involved in producing our Arenig
shell beds. Rather, we favour a high shell production rate in a
nutrient-rich environment on a new layer of ash during a period of
quiescence between volcanic eruptions. As such, we have adapted the lead
of Kidwell (1986).

Correlatives of the Lower Birch Island Member

The felsic volcanic rocks of the Shin Brook Formation are a
lithological and time correlative of the Lower Birch Island Member of
the Turnbull Mountain Formation, despite the marked difference in unit
thickness and texture of the volcanic rocks. These volcanic rocks in the
Shin Pond quadrangle consist of a maximum of 750 m from the base to a
cap of a metadiabase sill at the top of the exposed sequence. The sill
has intruded the Shin Brook strata and perhaps, but not assuredly, is of
Shin Brook age (Neuman 1967). Above the local pebble conglomerate, the
Shin Brook Formation consists of felsic tuff, breccia and volcanic
sandstone. Most common is grey to greenish grey feldspar-phyric lapilli
tuff in thick and thin beds. Rare are probable flows and ignimbrite.
Slate, siltstone and sandstone consisting entirely of volcanic detritus
form a minor part of the formation. What proportion of the felsic tuff
is simply water-lain or was carried in water for at least a short
distance as a turbidity current, slurry or mass flow is difficult to
estimate. Indeed, all of the tuffaceous rocks with fossils were
deposited in water as well as those probably lacking fossils. Some
volcanic sandstone (sandy tuff) beds are richly fossiliferous with
brachiopods, some trilobites and bryozoans and rare gastropods (Neuman
1964). Some beds grade upward from coarse- to fine-grained sandstone and
others from fine-grained sandstone to slate. Exotic rock fragments have
not been recognized. The Shin Pond volcanic rocks extend into the
adjacent Island Falls quadrangle where they are as much as 300 m thick
and consist of slaty felsite, coarse-grained calcareous tuffaceous
sandstone and ash-flow tuff (Ekren and Frischknecht 1967). Volcanic
rocks in the Mount Chase belt, mainly basalt lavas and sills plus slate
and pyroclastic rocks, are exposed in a fault-block several kilometres
to the southeast of the Shin Brook volcanic belt. They have been
interpreted to overlie the Shin Brook Formation and are presumed to be
of the same age at least in part (Ekren and Frischknecht 1967).

In the northeastern Miramichi Highlands, volcaniclastic strata of
the Little Falls Member of the Nepisiguit Falls Formation, overlying the
Vallee Lourdes Member along the Tetagouche River, is a lithological and
time correlative of the Lower Birch Island Member but lacks brachiopods
and is much thicker. There, about 30 m of thick-bedded, medium- to
fine-grained, quartz-feldspar-crystal-rich volcaniclastic sandstone,
crystal tuff and ash tuff of the member have been interpreted as a
sedimentary sequence (Little Falls section; Fyffe et al. 1997). A
hand-picked sample of needle-like zircons (amongst a varied population)
extracted from quartz-feldspar crystal tuff of this unit near Tetagouche
Falls 1.7 km west of Little Falls, and believed to be essentially free
of an inherited component, yielded a concordant age of 471 [+ or -] 3
and 469 [+ or -] 9 Ma ((206)Pb/(238)U and (207)Pb/(235)U, respectively).
Zircons from near the top of the formation 25 km to the south yielded a
concordant age of 469 [+ or -] 2 Ma (Sullivan and van Staal 1996). The
interpreted age of the Nepisiguit Falls Formation is 470 Ma, i.e. middle
to late Arenig if the Arenig extended from about 480 to 465 Ma (McKerrow
and van Staal 2000). The age of the brachiopod-bearing Vallee Lourdes is
thus constrained to the Arenig, probably late Arenig, along with the
volcanic rocks of the Little Falls Member. Confirmation of these ages is
provided by the overlying Flat Landing Brook Formation of felsic flows,
pyroclastic rocks and interlayered tholeiitic basalts and maroon shales
and siltstones (van Staal et al. in press). Three U-Pb zircons ages from
the formation indicate a late Arenig to early Llanvirn age. It thus
seems most probable that the Upper Buttermilk and Lower Birch Island
members of the Turnbull Mountain Formation are also late Arenig age or
possibly middle to late Arenig age.

In summary, the Turnbull Mountain Formation with its two members of
differing lithology varies across the Napadogan area. The Upper
Buttermilk quartzite conglomerate occurs only in the northwest, and
probably originated by uplift and erosion of Miramichi light grey
mudstone and sandstone along a rift fault or faults accompanying the
hypothetical Napadogan uplift located probably southeast of the Otter
Slide and Burnt Hill belts in their original Arenig pre-thrust
positions. Vigorous stream erosion and transport deposited the gravel on
submarine stream fans. The gravel subsequently flowed northwestward into
deeper water through submarine canyons that were cut into the outer
edges of the uplifted belt. Earthquakes associated with rift-related
faulting and volcanism triggered the slumping. Canyon transport is
believed to account for local, lenticular distribution of the
conglomerate. Meanwhile, southeast of the uplift, turbidity currents
from the southeast may have continued to deposit Miramichi Group
sediments on the continental slope. No interbedding of conglomerate and
fine-grained Miramichi Group strata has been observed. The overlying
Lower Birch Island Member also varies widely from place to place across
the Napadogan area. Felsic volcanic rocks are exclusively tuffs, are
thickest in the northwest and are absent to the southeast where
fine-grained, non-volcanic sediments take their place with a mix of the
two in the middle (Lower Birch Island type locality). A mafic flow (or
flows) occurs locally in the southeast, but elsewhere the minor mafic
volcanic rocks appear to be only tuffs. Mafic tuff and flows are much
more abundant within several tens of kilometres to the northeast of the
Napadogan area. These relations support a model in which the three belts
within the Napadogan area represent thrust slices brought together from
the northwest and from more widely separated locations than currently
positioned.

The siltstone and mudstone deposited to the southeast of the
Napadogan uplift was probably derived from the Napadogan uplift to the
northwest along with their Celtic fossils. Perhaps a less likely source
is to the southeast as a continuation of Miramichi sedimentation. In
either case, the resulting strata could be lithologically the same.

BRACHIOPODS

Brachiopods of late Arenig age have been found in seven localities
in the Napadogan area, all in the Lower Birch Island Member. Below is a
description of each site and the history of identifications as
understanding of the age of the assemblage developed through 130 years
of paleontological research. Then will follow a summary table of the
current view on identification and some notes on the genera.

Rocky Brook locality

The first known brachiopod locality in the Napadogan area, the
Rocky Brook locality, was discovered by Edward Jack, a civil engineer
and land surveyor, who in 1867 "communicated that fact [existence
of the fossil locality] in a short note to the Natural History Society
of St. John (sic.)." (Robb 1870, p.190). The locality is located on
an unnamed tributary that flows westward into Rocky Brook (that joins
the Nashwaak River) 0.5 km south of Valley Forest road (Fig. 2; Poole
1958; Crouse 1981b). The locality is 1.2 km due east of the mouth of the
tributary (zone 19 659680E 513282N FB). Charles Robb was led to the
locality by Jack in 1868. Elkanah Billings identified from Robb's
collection (GSC loc. 3157): Chonetes canadensis, Leptocoelia
flabellites, Renssellaria ovoides, Strophomena perplana, and
Streptorhyncus sp. indet., and correlated the rocks with the Upper
Silurian and Devonian Gaspe limestones (Robb 1870). The locality became
a small belt of Silurian-Devonian within a broad area of unfossiliferous
strata presumed to be Cambro-Silurian, later known as Ordovician (Bailey
et al. 1886). Poole recollected the locality about 90 years later, in
1957 (GSC loc. 32399), and L.M. Cumming identified: ?Tritoechia sp. or
?Schuchertella sp., Hesperonomia? sp., brachiopod genus A and brachiopod
genus B. He interpreted the age as Ordovician or Silurian and observed
that some brachiopods resembled those from the Lower Ordovician Luke
Hill Formation of southern Quebec (Globensky 1981; GSC internal report O
of S-3-57/58-LMC). In 1959, Poole led Cumming and A.J. Boucot to the
locality, and Boucot orally declared the locality not to be Silurian or
Devonian but Ordovician. From the resulting collection (GSC loc. 40749)
Cumming identified: Orthambonites sp., Dictyonema sp., ?Reuschella sp.
cf. R. horderleyensis, and ?Dolerorthis sp. (GSC internal report
O-1-1963-LMC). In the same report, he recorded: "Professor Alwyn
Williams...briefly examined this collection during April 1962 and voiced
the opinion that the brachiopods were Ordovician forms and probably
Caradoc in age." Cumming noted that Orthambonites is Lower to
Middle Ordovician. During 1966, Neuman examined the fossils in GSC loc.
40749 and identified: Orthambonites, Productorthis, Tritoechia,
?Taphrorthis, and a new genus of syntrophid (Neuman, written
communication to Cumming, 1967). Neuman collected the locality in 1967
and identified: new genus aff. Glossorthis (13 specimens), new genus
aff. Henellina (21), Orthambonites sp. (35), Porambonites sp. (4),
Productorthis sp. (2) and Tritoechia sp. (11) (Neuman, written
communication to R.R. Potter, 1968). In a subsequent publication, Neuman
(1968) grouped all brachiopods identified from the Rocky Brook, Lower
Birch Island and Middle Hayden localities as: Productorthis mainensis
Neuman (uncertain species identification), Orthambonites robustus Neuman
sp., Valcourea sp., Tritoechia billingsi Neuman, new genus of syntrophid
and Eodalmanella sp., and suggested that they were probably Llanvirn in
age. A sample for conodont search, collected in 1978 by G.S. Nowlan and
Poole (GSC loc. 96069), proved to break down poorly and was found to be
barren of conodonts (Nowlan 1981). Neuman (1971, 1984) listed all the
brachiopods together from the Rocky Brook, Lower Birch Island and Middle
Hayden Brook localities; those on the list appearing in Neuman (1984)
(and in brackets, the new species described by Neuman 1971), are:
Munhella (M. cummingi Neuman), Orthambonites, Productorthis, Tritoechia,
Fistulogonites, Schedophyla (S. potteri Neuman) and Rugostrophia (R.
sylvestris Neuman). Neuman (1971) interpreted the age as Arenig and
Neuman (1984) stated Arenig but late Arenig for the Shin Brook
Formation. To our knowledge no other collections from the Rocky Brook
locality have been made and studied since 1978.

Lower Birch Island locality

The second brachiopod locality discovered in the Napadogan area,
the Lower Birch Island locality, occurs at the type section of the Lower
Birch Island Member and is located along the east shore of the S.W.
Miramichi River, 400 m north (upstream) of Lower Birch Island (Fig. 2;
zone 19 68614E 516032N FB). Fossil shells were first noted by R.W. Ells
in 1880 as "imperfect fossils at one point" but he did not
collect them (Ells 1881, p. 22D). A compiled regional map, 1 inch to 4
miles, published a few years later (Bailey et al. 1886), does not
indicate the locality, but a fossil symbol marked 4 km downstream, may
have been misplaced on the map. Some years later, Bailey (1906)
relocated and collected the locality. Ami (1906) remarked on the
fragmentary nature and poor preservation of the fossils (GSC loc. 2141),
and identified: Orthis sp. indet., Rhynchonella sp., Homoeospira sp.,
Lingula sp. and Spirifer sp., and stated the collection "may be
Silurian". More than 50 years later, Poole recollected the locality
1957 (GSC loc. 32398; Poole 1960) and Cumming identified: Orthis sp. cf.
O.panderiana Hall and Clarke, brachiopod genus A, brachiopod genus B and
brachiopod genus C (GSC internal report O or S-3-57/58-LMC). Genus A and
genus B were also found at the Rocky Brook locality. Cumming was
uncertain whether the collection was Silurian or Ordovician, but, as
with the Rocky Brook locality, he seemed to favour an early Ordovician
age. Neuman examined some GSC collections on loan in 1966-67 and
reported to Cumming that he identified Orthambonites (Neuman, written
communication to Cumming, 1967). Later during 1967, Neuman visited the
locality, guided by R.R. Potter, and identified: new genus aff.
Aporthophylla (2 specimens), new genus aff. Glossorthis (1),
Orthambonites sp. (6), and Productorthis (1) (Neuman, written
communication to Potter, 1968). Neuman (1968, 1971, 1984) grouped all
brachiopods from the Rocky Brook, Lower Birch Island and Middle Hayden
Brook localities, as described above, under the Rocky Brook locality. In
1978, Nowlan and Poole collected the locality for a conodont search.
Unfortunately, sample GSC loc. 96066 broke down poorly in acids,
yielding only "two simple cone elements assignable to the form
genus Oistodus Pander" and was of little use in determining an age
(Nowlan 1981).

In 2002, Poole collected two samples of coarse, recrystallized
calcarenite discovered in blocks of calcareous siltstone that had
slumped to the shore from uphill exposures near the type locality.
Fortunately the samples yielded conodonts that, although fragmentary, do
clearly constrain the age of the brachiopods to late Arenig. Nowlan
reported (GSC internal report 004-GSN-2003) that one sample (GSC loc.
O-18217) yielded Protopanderodus sp. (one specimen) and Tripodus sp.
(7), and the second sample (GSC loc. O-108218) yielded Drepanoistodus
sp. (1) and Tripodus sp. (10), all thermally altered to CAI 5. Nowlan
commented on both samples: "This modest fauna of simple cone
elements is the first identifiable conodont material to be recovered
from this locality that yields late Arenig brachiopods (see Nowlan
1981). The specimen assigned to Protopanderodus sp. is most similar to
Protopanderodus rectus (Lindstrom). The fauna is dominated by specimens
assigned to Tripodus. The type species of this genus is Tripodus laevis
Bradshaw, the zonal index for the base of the Whiterock Series in North
America. The present material is not conspecific with T. laevis but is
likely a separate species. Several occurrences of other species of
Tripodus are known, although none is formally named. For example, the
genus is known to occur in the Latorp Limestone of Arenig age in Sweden
(personal communication R.L. Ethington and comparative specimens
examined) and in the upper McKay Formation and lower Glenogle Formation
in British Columbia (Norford et al 2002). The specimens recovered herein
are similar to the forms present in the Latorp and Glenogle formations
which are of late Arenig age (D. bifidus graptolite Zone and O. evae
conodont Zone), slightly older than the base of the Whiterock Series.
The age of the sample is therefore late Arenig (Blackhillsian; late
Ibexian in North American stadial nomenclature)." To our knowledge,
no other fossil collections and studies have been carried out at the
locality.

From 1997 to 2000, four new brachiopod localities were discovered
and were named for convenience the North Taxis Road, Turnbull Mountain,
Long Hill and Headwaters of Middle Hayden Brook localities (Fig. 2). The
first three are situated along a line 3 km long in the northwestern
Napadogan area, representing the trace of the Lower Birch Island Member,
sliced and separated by strike faults along the eastern edge of the
Otter Slide belt (Fig. 3). The fourth lies 5 km to the northeast within
the similarly sliced, southwestern end of the Burnt Hill belt (Fig. 4).
Brachiopods from all four localities are moulds and many details have
been lost by dissolution of carbonate in the current weathering zone.
The lack of a carbonate host rock severely hindered a search for
conodonts.

North Taxis Road locality

The North Taxis Road locality, the first found of the four, was
discovered by Poole in 1997. It occurs along a logging road, referred to
informally by Poole as the North Taxis road (Fig. 3), 1.1 km southeast
of the junction with the main Napadogan haulage road that leads 7 km
south to the Bowater gate at Napadogan (i.e. about 1.4 km at
045[degrees] azimuth from Turnbull Mountain; zone 19 66165E 5147732N
FB). The locality consists of broken outcrop and rubble of weakly
cleaved, massive, light yellow-grey felsic tuff, aphanitic to sand-size
and aphyric, of the Lower Birch Island Member, in a partly slumped
half-metre wall along a roadside ditch on the south (uphill) side of the
road. The fossil collection (GSC loc. O-108123) was examined by Neuman
who identified in decreasing order of abundance: Schedophyla potteri
Neuman, 1971; Productorthis mainensis Neuman, 1964; Rugostrophia
sylvestris Neuman, 1971; and small numbers of specimens that resemble
Tritoechia and Paralenorthis but cannot be confidently identified
(Neuman, written communication to Poole, 1998). He commented further:
"Most of the Schedophyla specimens are as much as twice the size of
those from the Middle Hayden Brook locality, and their imbricated shells
pave bedding surfaces of some of the blocks in the sample to the virtual
exclusion of other forms. All specimens appear to be disarticulated, and
ventral valves are far more common than dorsals, perhaps a 10:1 ratio.
[This situation] appears to be the result of sorting and distribution by
water currents. Many Productorthis specimens from other layers are
articulated, an indication of weaker currents. The few large
Rugostrophia shells are all disarticulated.

"Beyond New Brunswick, Schedophyla has also been identified in
Arenig/Llanvirn-age assemblages in southern China (Rong Jia-Yu, Nanjing
Institute of Paleontology and Geology, written communication,
1987)."

Turnbull Mountain locality

The Turnbull Mountain locality was found by Poole during 1997
shortly after the North Taxis Road locality (Fig. 3). It is located 1.3
km south of the North Taxis Road locality, along an old logging road on
the eastern side of Turnbull Mountain, about 0.8 km at 104[degrees]
azimuth from the top of Turnbull Mountain (zone 19 66152E 514598N FB).
The locality consists of rubble exposed where road building had removed
the organic layer and some of the thin till layer many years previously.
The fossils occur in massive, aphyric felsic tuff rubble, light greenish
grey to creamy grey, of the Lower Birch Island Member, almost identical
lithologically to the North Taxis Road locality. The fossiliferous
layer, about 3 cm thick, is cut by a weak cleavage about 45 degrees to
the layer and, given that the cleavage in nearby bedrock is steep, the
fossil layer dips moderately. Hand trenching revealed that some of the
rubble lies above barren glacial till 20 to 30 cm below the surface.
Evidently, the "rubble" has been moved a short distance into
place above till by glacial ice. As interpreted from rubble, the one
metre of tuff is faulted on the southeast against Caradocian dark grey
slate-chert and is underlain by nearly 2 metres of weakly cleaved,
massive and weakly laminated slate, light green-grey to light grey, to
the end of the trench in till. Most of the brachiopods were collected
from the tuff layer and only a few fragmentary brachiopods from the
underlying slate. The first collection (GSC loc. O-108124) was examined
by Neuman who identified aff. Eostrophomena sp. of McKerrow and Cocks
(1977, 1986) (Neuman, written communication to Poole, 1998). He
commented: "These specimens are plainly conspecific with the
specimens from the Davidsville Group at Gander Lake, Newfoundland
(Blackwood 1982) that remain in "open nomenclature" despite
having been identified as a 'Celtic Province' orthid and
illustrated twice by McKerrow and Cocks (1977, 1986). Specimens that
would permit confident taxonomic analysis are not yet in hand".
Neuman and Poole recollected the locality in 1998 (GSC loc. O-108196)
and later that year Poole hand-trenched the locality for stratigraphy.
More from the same layer were sent to Neuman (GSC loc. O-108196) as well
as a few fragmentary brachiopods from the underlying slate (GSC loc.
O-108197). Neuman reported (oral communication to Poole, 1998) that he
identified Eostrophomena and bryozoa in the collections as well as two
specimens of a large, unknown brachiopod, that may be Ukoa sp., poorly
described by Opik (1932). During 1999, Neuman, W.H. Forbes and Poole
hand-trenched the Turnbull Mountain locality with renewed diligence in
search of Ukoa? (GSC loc. O-108209). From this collection, Neuman
identified Monorthis sp. and many specimens of Ukoa?, both dorsal and
ventral valves (Neuman, written communication to Poole, 1999).

Long Hill locality

The third locality was found in 1998 by Neuman when Poole led him
and Fyffe to promising aphyric felsic tuff of the Lower Birch Island
Member lying above a quartzite conglomerate. The tuff seems to be
identical to that in the two above localities. The locality occurs on an
old logging road that runs straight northwesterly up a knob lying next
to and southeast of Otter Slide Mountain (Fig. 3). The locality is
located 0.45 km at 294[degrees] azimuth from the junction of the main
Napadogan haulage road and the Upper Hayden road leading to the Mine
road (zone 19 66182E 514892N FB). Neuman found a single mould of a
small, coarsely ribbed brachiopod in a loose piece of tuff that he
intentionally left at the locality.

Headwaters of Middle Hayden Brook locality

The last locality was found in 2000 by Poole on an old logging road
0.57 km at 185[degrees] azimuth from a crossroad junction of the Mine
road and the Slate Island road/Lower Hayden road (Fig. 4; zone 19 66532E
515287N FB). Fragments of brachiopods were found scattered along 11
metres of the road in loose pieces of quartzose sandstone, slate and
some granule conglomerate. The fossiliferous sandstone appears to be
less than a few metres stratigraphically below crystal tuff. Neuman
determined that the collection (GSC loc. O-108216) contains fragments of
brachiopods and that none could be identified (oral communication to
Poole, 2000).

Current identifications

Only four of the seven brachiopod localities in the Napadogan area
have yielded confidently-identifiable brachiopods. Brachiopods from the
other three localities (Lower Birch Island, Long Hill and Headwaters of
Middle Hayden Brook) on reconsideration, are either too deformed or too
fragmentary, but they are consistent with the identifications of the
four. The loss of calcitic details of the brachiopods in weathered
specimens prohibits identification at the species level. Generic names
of brachiopods are arranged alphabetically in Table 1 by host formation
and enclosing lithology.

Dolerorthis sp. replaces the name Munhella of Neuman (type species
M. cummingi, 1968) following Williams and Harper (2000, p.740) in their
finding that the latter generic name is an invalid junior synonym.

Monorthis cf. M. typis Bates, 1968. The type species of the genus,
M. typis Bates, was based on poorly preserved specimens from
coarse-grained sandstone of probable late Arenig age from the
Treiorwerth Formation of Anglesey in northwestern Wales, the only
occurrence known at that time. The genus, as M. cf. M. menapiae
(Davidson), was later reported in carbonate rocks of the San Juan
Limestone of the Precordillera in northwestern Argentina (Herrera and
Benedetto 1991; Benedetto 2001b). Well-preserved congeners from the
volcanic-rich Suri Formation of the Famatina Range in northwestern
Argentina (Benedetto 1994) provide information that confirms this
identification. Poorly preserved, deformed specimens that may belong to
this genus occur in the Davidsville Group of Newfoundland, identified as
"aff. Eostrophomena sp." by McKerrow and Cocks (1986). See
Hatcher (1990, p. 87) for a photograph of a bedding surface of deformed
specimens from the Davidsville Group near Gander, Newfoundland.

"Paralenorthis?" Reassignment of coarse-ribbed shells
formerly assigned to Orthambonites (Neuman 1968) follows Jaanusson and
Bassett (1993) in their use of the name for specimens from the Shin
Brook Formation of Maine. In the absence of the features that permit
their discrimination from similarly ornamented shells,
"Paralenorthis" is used here for medium to strongly costate brachiopods, formerly referred to as Orthambonites. Many of the
characters that permit their recognition are not preserved in specimens
from these localities, but the characteristic features that permit
discrimination of the genus can be seen in some specimens from the Shin
Brook Formation (Jaanusson and Bassett 1993).

Productorthis has been identified at most of these localities from
external moulds that preserve its characteristic ornament of imbricated
growth lamellae and other features. It has been identified in the
Treiorwerth Formation of Wales, and in other Celtic assemblages such as
the Shin Brook Formation of Maine and, in Newfoundland, the Summerford
Group of New World Island (Neuman 1976) and the Indian Bay Formation
(Wonderley and Neuman 1984).

Rugostrophia is distinctive and quite abundant in outcrop on Middle
Hayden Brook, the source of the type specimen of the species (R.
sylvestris) and the genus that was erected to contain it. The genus is
also present in the Summerford Group of Newfoundland (Neuman 1976), in
the Treiorwerth Formation of Wales (Neuman and Bates 1978) and in
volcaniclastic rocks of western Puna in northwestern Argentina
(Benedetto 2001a).

Schedophyla is the most common fossil in the North Taxis Road
locality, particularly where moulds of its shells together with smaller
numbers of ramose and encrusting bryozoans pave bedding surfaces.
Reported also from northwestern China (Xu and Liu 1984, cited by Cocks
and Rong 1989).

Skenidioides is a small shell collected at the Middle Hayden Brook
locality that occurs in Celtic assemblages in the Treiorwerth and
Nantannog formations of Anglesey (Bates 1968) and in volcaniclastic
rocks of the Suri Formation in northwestern Argentina (Benedetto 1994).

Tritoechia is known from only one specimen from all of these
localities, the Tetagouche River locality, but it is common in Celtic
assemblages elsewhere and in carbonate rocks of the Laurentian platform.
The one specimen here is unique for its preservation as an external
mould of the two conjoined valves, that, when collected, was filled with
large crystals of calcite that were dissolved in the laboratory.

"Ukoa" sp. indet. refers to the nearly forty specimens
from the Turnbull Mountain locality of a large dorsibiconvex,
fine-ribbed shell, many of whose characters are not preserved (Fig. 11).
The name itself is used with uncertainty because the original
description (Opik 1932) neither mentioned nor illustrated features of
the cardinalia that are essential for its classification (see Cocks and
Rong 1989, p. 150). We are seeking assistance of colleagues to solve
this problem.

[FIGURE 11 OMITTED]

DISCUSSION AND CONCLUSIONS

The relatively thin Arenig strata of Napadogan area vary markedly
from southeast to northwest: argillite in the southeast (Rocky Brook and
Middle Hayden fossil localities) through siltstone with thin felsic tuff
interbeds (Lower Birch Island fossil locality) to thicker felsic tuff
and underlying minor argillite and sandstone in the northwest (Otter
Slide and Burnt Hill belts). The sedimentary strata in all these
localities lack volcanic detritus. The volcanic rocks are tuffs (except
for a local basalt flow on Middle Hayden and Lower Hayden brooks) and
probably were derived from volcanism farther to the northwest beyond the
limits of the Napadogan area. The exposures of Arenig strata are parts
of probable thrusts from the northwest juxtaposed from their original
depositional sites.

The location of source areas and the mode of deposition of the
sedimentary strata are conjectural. The Upper Buttermilk quartzite
conglomerate in the northwestern Napadogan area was probably derived,
not from a relatively non-rifted Gander margin to the southeast of the
Napadogan area, but from a hypothetical, subaerial, short-lived,
rift-related uplift, herein named the Napadogan uplift, located during
the Arenig between strata of the Otter Slide-Burnt Hill belts and of the
Lower Hayden belt. The quartz-sandstone pebble and cobble gravel was
derived from the light grey facies in the upper beds of the Miramichi
Group, was probably first deposited on local submarine fans off vigorous
streams, and later flowed as mass submarine slumps northwestward down
submarine canyons to come to rest as lenses of gravel in water depths
where oxic, light grey and anoxic, dark grey Miramichi facies were
interlayered. Erosion was deep enough to reach consolidated sandstone
but not deep enough to reach quartz veins and penetratively deformed
sandstone, if any then existed, nor to reach basement rocks beneath the
Miramichi strata. Slumping was triggered probably by earthquakes caused
by faulting and volcanism. The conglomerate of the Tetagouche Group and
Shin Brook Formation may point to a zone of nearby rift faults and thus,
a zone of higher probability of the occurrence of volcanogenic massive
sulphide deposits if such deposits in a back-arc setting are indeed
spatially and genetically related to rift faults and volcanism. No such
faults have been recognized in the Miramichi and Lunksoos terranes,
because they would probably be sites of younger faults, thus obscuring
their earlier history.

The much different, polymictic pebble to boulder conglomerate at
the base of the Shin Pond Formation in the Island Falls quadrangle and
of the Vallee Lourdes Member along the Tetagouche River near Vallee
Lourdes requires a mixed quartzite and volcanic source area. We suspect
the structurally overlying, obducted Penobscot Arc rocks, but we must
await geochemical and isotopic studies by others for confirmation or
otherwise of this speculation.

Within the Napadogan area, felsic tuffs are thicker and coarser
textured in the northwest and thin southeastward to intercalated
fine-grained tuff less than a few centimetres thick in siltstone in the
"middle" Napadogan area (Lower Birch Island locality) and then
to zero in southeastern Napadogan. Celtic brachiopods and associated
fauna within tuffs and associated strata probably lived along the flanks
of the Napadogan uplift, became smothered by periodic, airborne volcanic
ash falls, and quickly reoccupied the buried sites. The ash settled into
relatively deep water at or just below wave base, and was not reworked
by water currents. Soon after primary deposition and before
consolidation by diagenesis, the ash may have undergone minor slumping.
The volcanic source lay somewhere to the northwest of the Napadogan
area. The Lunksoos area by virtue of its much thicker and coarser
volcanic assemblage was probably closer to a hypothetical belt of
volcanism lying between the general areas of Lunksoos and Bathurst
during the Arenig. The core of the hypothetical belt in its
post-thrusting location may be marked by early Ordovician granitic
bodies extending from the Rockabema granite in the Lunksoos area to
several in the central and northeastern Miramichi Highlands.

The fine-grained strata with Celtic brachiopods of the Lower Hayden
belt were probably derived from recycled Miramichi strata on the
Napadogan uplift to the northwest. They are conformable with the
underlying Miramichi Group strata, contain detrital muscovite like the
Miramichi Group, and lack volcanic detritus. They were probably
deposited in relatively deep water, below wave base, between the
Napadogan uplift and the southeastern source of Miramichi strata on the
Gander margin.

The few genera of brachiopods of late Arenig age from the Miramichi
and Lunksoos anticlinoria are part of the Celtic bio-geographic
assemblages typical of cool waters in high southern latitudes in
contrast to the coeval Toquima-Table Head assemblage typical of warm
waters in low southern latitudes (Williams 1973; Neuman 1984). These
distinctive assemblages together with the paleomagnetic signatures of
relevant rocks permitted the paleogeographic reconstruction of the
Iapetus paleo-ocean (Harper et al. 1996), but do not incorporate
information beyond the Iapetus basin such as northwestern China (Xu and
Liu 1984) and recently published information from northwestern Argentina
(Benedetto 1994, 2001a). Both of these latter areas have brachiopods
that are remarkably similar to those of the Iapetan Celtic assemblages.
The terrane in northwestern Argentina is believed to be part of a small
Laurentian fragment that rifted away during the Early to Middle
Ordovician from the Southern Appalachian margin and accreted to Gondwana
by the Late Ordovician (Benedetto 2001b).

Localities of these Celtic brachiopods are rare along the
Appalachian-Caledonian belt: many localities in the Shin Brook felsic
volcanic rocks of the Lunksoos area were first discovered in the
northern Appalachians (Neuman 1964), seven localities in the Napadogan
area of the central Miramichi Highlands (Fig. 2), one locality along the
Tetagouche River in the Bathurst area of northeastern Miramichi
Highlands (Fig. 1; Fyffe et al. 1997), several localities in
Newfoundland (Wonderley and Neuman 1984; Boyce and Williams 1995;
Williams, S.H. et al. 1995), but nowhere in the central and southern
Appalachians. In Europe, Celtic brachiopods have been found in eastern
and southeastern Ireland, in Anglesey (Wales), and in Norway.

We assume that all brachiopods from the Lower Birch Island and
Vallee Lourdes members and Shin Brook Formation of the Miramichi and
Lunksoos terranes are of the same age from a paleontological
perspective. The low diversity of all localities and the poor
preservation of fossils in the Miramichi Highlands make impossible the
identification of same-age localities and distinguishing those that
differ enough to suggest a different age.

The paleontological age of the brachiopods themselves has been
interpreted conservatively as late Arenig-early Llanvirn with a strong
emphasis on the late Arenig. These Celtic assemblage brachiopods in the
Miramichi and Lunksoos terranes can be tied only loosely to strata whose
age is known from other fossils. Conodonts from the Middle Hayden Brook
locality were interpreted as "may range from early Middle Arenig to
earliest Llanvirn" (Nowlan 1981), thus supporting the earlier
interpretation of Neuman but not constraining it. In the Bathurst area,
conodonts from limestone and siltstone, from 20 to 25 m above the basal
conglomerate and roughly equivalent to the calcareous siltstone carrying
brachiopods a few kilometres to the west (Fyffe et al. 1997) yielded
only two poorly preserved conodont elements of middle Arenig to Llanvirn
age (Nowlan 1981). In the Napadogan area, a unit of manganiferous
slate-chert overlying the Turnbull Mountain Formation is barren of
fossils except for one exposure of dark grey slate-chert, on Turnbull
Mountain, where D.V. Venugopal in 1986 found poorly preserved
graptolites. John Riva determined that they were Llanvirnian (written
communication to Poole 2001). However, the calcarenite samples from the
Lower Birch Island locality collected during 2002 have yielded late
Arenig conodonts to G.S. Nowlan (GSC internal report 004-GSN-2003).
Paleontologically, the Celtic brachiopods and associated conodonts of
the Napadogan area are late Arenig.

Supporting this age are U-Pb zircon ages of ca. 471 and 469 Ma from
the lower and upper levels of the overlying quartz-feldspar crystal tuff
in the northeastern Miramichi Highlands. They are middle to late Arenig
(Sullivan and van Staal 1996), if the Arenig lasted from 480 to 465 Ma
(McKerrow and van Staal 2000). Thus, the minimum age of the Lower Birch
Island and Vallee Lourdes members and probably Shin Brook Formation is
late Arenig.

Miramichi-Grand Pitch strata must be looked to for an estimate of
the maximum age of the brachiopod-bearing strata. The Grand Pitch is
barren of fossils but for the trace fossil Oldhamia, suggestive of a
Cambrian age (Neuman 1962) and more recently shown to range from late
Precambrian to Middle Cambrian (Hofmann and Cecile 1981). The Baskahegan
Lake Formation in New Brunswick yielded ichnotaxa suggestive of an early
Ordovician age and is overlain by the Bright Eye Brook Formation of
black slate that has yielded late Tremadoc to earliest Arenig
graptolites in two localities 9 km apart (Bailey 1901; Fyffe etal. 1983;
Pickerill and Fyffe 1999). Both formations are believed to be equivalent
to parts of the Miramichi Group and Grand Pitch Formation, and the
Bright Eye Brook Formation is presumed to correlate lithologically with
at least part of the black slate-rich uppermost part of the
Miramichi-Grand Pitch strata.

The Miramichi Group in the Napadogan area has not yielded fossils
or volcanic rocks, but the uppermost unit, the Patrick Brook Formation
in the northeastern Miramichi Highlands, has a local, thin rhyolite near
the top that has yielded a U-Pb zircon crystallization age of 479 [+ or
-] 6 Ma (McNicoll et al 2002), i.e. some time between the middle
Tremadoc and middle Arenig when the error range is considered. This age
brackets the graptolite ages of the Bright Eye Brook Formation black
slate.

If these postulated regional correlations are correct, then the
Lower Birch Island and Vallee Lourdes members and the Shin Brook
Formation must be no older than middle Arenig. Middle to late Arenig
seems to be the best estimate at present of the ages of these sequences
and brachiopods. This estimate is supported by fossils and stratigraphy
of the Treiorwerth Formation in northwestern Wales (Fortey et al. 2000).

One feature common to many Arenig fossil localities in the
Miramichi Highlands is the low diversity of brachiopods within the
collections. For example, one collection may be dominated by one
brachiopod species and only a few kilometres along strike, a different
brachiopod species dominates. And in one of our localities, a densely
populated shell bed carrying one brachiopod species is separated by a
few centimetres of sandy tuff from another shell bed dominated by
another brachiopod species (see Fig. 11 caption). Admittedly, the
Napadogan fossiliferous beds are thin and may not characterize diversity
properly. Nevertheless, we suspect that such low diversity in the
Miramichi collections is the result of the rapid colonization response
to opportunities for expansion by individual brachiopod species along
the outer shelves bordering rift-uplifts and volcanic islands in a
non-uniform, rapidly-changing environment of sedimentation, volcanism
and burial by ash in relatively deep water with relatively narrow
uplifts and subsidence along the rift zone during the development of the
back-arc basin. In such a scenario, environments favouring brachiopod
colonization (e.g., bottom character, currents, salinity, oxygen
content, water temperature, nutrients, no competitors or predators) were
created from an unpopulated environment. A shell bed, so well developed
in the Shin Brook Formation and to a minor extent in the northwestern
Napadogan area, probably resulted when a successful brachiopod species
colonized new surfaces on a fresh volcanic ash layer during a period of
volcanic quiescence in a nutrient-rich environment. By contrast, the
Celtic Arenig fossil localities of the Summerford Group in north-central
Newfoundland are highly diverse. The Summerford volcanic rocks are
tholeiitic and alkalic basalts, and are believed to have been formed as
seamounts on an ocean floor (Jacobi and Wasowski 1985). Associated
sedimentary rocks are carbonate, greywacke and mudstone. The tectonic
environment is unlike that of the Napadogan-Lunksoos areas.

The Napadogan area during the Arenig seems to have been on the
fringe of volcanism and sub-volcanic plutons, and by extension, of
intense rifting and uplift-subsidence. We suggest the Napadogan rocks
lay outside of, and to the southeast of, most of the zone of rifting,
etc. characteristic of the Lunksoos area and northeastern Miramichi
Highlands.

Reconstructions of the distribution of land masses and oceans
during the Arenig universally place the Gander margin of the
Miramichi-Lunksoos area, and parts of Newfoundland and the British
Isles, in southern latitudes with cool waters, about Lat. 45[degrees]S
to 60[degrees]S, adjacent to Gondwana (Neuman 1984; Scotese and McKerrow
1991; van Staal et al. 1998). The Laurentian margin is placed in warmer
waters in low southern latitudes, about Lat. 20[degrees]S to
30[degrees]S. The Iapetus Ocean lies between the two and is perhaps 20
to 30 degrees of latitude wide, or about 2000 to 3000 km.

Such a distance is believed to be more than adequate to prevent
brachiopod larvae from colonizing the far side of Iapetus. More mature
brachiopods, however, could be carried on floating pumice in circulating
ocean currents resembling the modern Gulf Stream. Successful long-range
colonization requires tolerance for differing environments. The
existence of a Celtic paleogeographic assemblage during the Arenig
implies evolution in isolation, protected from invading
"foreign" brachiopods and predators by an ocean barrier
and(or) intolerance of new conditions on arrival. We reiterate Neuman
and Harper's (1992) support of the existence of the Celtic
assemblage, in spite of Cocks and McKerrow's (1993) reservations.

Poole is responsible for the geology presented here, and the author
of most of this paper. During field work from 1997 through 2002 he
enjoyed the hospitality of Bob and Karen Armstrong of Stanley, Rod and
Esther Flowers of Dorn Ridge and Douglas and Priscilla MacDonald of
Burtts Comer, for which he is grateful. He thanks the forest rangers of
the New Brunswick Department of Natural Resources and Energy in Stanley
for their support, and the staff of Minerals and Energy Division in
Fredericton, especially Les Fyffe, Rao Irrinki, and Greg Crouse whose
long experience with the geology of the Napadogan terrain led to many
enjoyable geological discussions. To this list must be added Dick Potter
who generously offered information and thoughts on the geology of the
Burnt Hill belt. Gary M. Boone of Presque Isle provided a specimen of
the quartzite conglomerate from the base of the Shin Brook Formation.
Avenor Pulp and Paper Ltd. and currently Bowater Canadian Forest
Products Inc., owners of the Freehold, kindly provided free access to
the logging road system. Poole thanks the Geological Survey of Canada
for support in the office and field since his retirement. Robert Kelly
improved the field photographs with his deft techniques, and Amanda
Chiprout patiently converted my crudely drawn figures into images
digestible and improvable by computer.

Neuman (1971) had collected and described brachiopods from this
area, having been led to relevant outcrops by Poole's colleagues
who were familiar with his work there. Poole's later work revealed
additional occurrences of fossils, which were sent to Neuman in
Washington. He joined Poole in New Brunswick to exploit these
discoveries in 1998 and with W.H. Forbes of Presque Isle, Maine, in
1999. The results of this work are presented in the paleontology section
of this paper which was written by Neuman. Neuman and Forbes kindly led
Poole to a few key outcrops in the Lunksoos area in 2000.

Our thanks to John Riva and especially to Cees van Staal, each of
whom critically reviewed early drafts and offered many useful comments
and follow-up discussion. Thanks also to journal reviewer Adrian Park
for his suggestions for improvement. We have special thanks to reviewer
Les Fyffe who has followed Poole's work over the years, has visited
"our" rocks from time to time, and diligently made many astute
and careful suggestions for improving the first draft. This, of course,
is not to say that Les agrees with our favoured positions on the
geology. Geological Survey of Canada Contribution 2002017.

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